It is often desired to combine magnetic resonance (MR) imaging and positron emission tomography (PET) in one unit to merge the high-resolution anatomical images provided by MR with functional information provided by PET. One difficulty in making a combined MR/PET system is that the RF transmit antenna of the MR system can produce deleterious effects on the photodetection electronics of the PET system. To avoid these deleterious effects, an RF screen (e.g., a continuous layer of copper) can be used to shield the photodetection electronics of the PET system from an RF antenna by placing all of the components of the PET system on the opposite site of the RF screen from the RF antenna. With this design, a larger-diameter gradient coil would be needed to provide the space needed for the components of the PET system. This greatly increases production costs, as the radial space inside a magnet tunnel is restricted and expensive. Another disadvantage to this design is that, because the RF screen is between the patient and the PET detector, the RF screen can attenuate gamma radiation emitted from the patient before it reaches the PET detector.
There is a need, therefore, for a combined MR/PET system that overcomes these problems.